1. Field of the Invention
The present invention relates to a keyless entry system that locks and unlocks doors of a vehicle by signal transmission from a portable transmitter, and more particularly, to a keyless entry system that can properly perform locking and unlocking even when the portable transmitter is operated a plurality of times in a short time.
2. Description of the Related Art
FIG. 4 is a schematic block diagram of a known keyless entry system that remotely locks and unlocks doors of a vehicle, such as an automobile, by transmitting a signal from a portable transmitter to an operation unit installed in the vehicle.
The keyless entry system shown in FIG. 4 includes a portable transmitter 50 in which a unique identification (ID) code is set and which is capable of wireless communication, and an operation unit 60 installed in the vehicle to lock and unlock the doors of the vehicle in response to a lock signal and an unlock signal received from the portable transmitter 50. In the operation unit 60, for example, a receiver 70 for receiving signals from the portable transmitter 50 is connected to a controller 80 that controls the operation of the vehicle, for example, opening and closing a power window.
A lock signal and an unlock signal are transmitted by an operation switch 53 including a lock switch 53a and an unlock switch 53b. The lock switch 53a is pressed to transmit a lock signal, and the unlock switch 53b is pressed to transmit an unlock signal. Each of the lock signal and the unlock signal is transmitted from the portable transmitter 50 for 400 msec. When the receiver 70 identifies the received lock or unlock signal as a signal transmitted from the predetermined portable transmitter 50, it outputs a lock command signal of 600 msec from a lock output 74 to the controller 80 in response to the lock signal, and outputs an unlock command signal of 600 msec from an unlock output 75 in response to the unlock signal.
When a command signal of 600 msec or more is input, the controller 80 determines that a predetermined command signal is input, and then drives an actuator 90 for 600 msec to lock or unlock the doors. In the locking operation, all doors are locked in response to a first lock command signal. In the unlocking operation, only a door beside the driver's seat is unlocked when a first unlock command signal is received, and the other doors are unlocked when a second unlock command signal is received within a predetermined time (e.g., five seconds) after the reception of the first unlock command signal. That is, the controller 80 drives only a motor 91 corresponding to the driver's seat door when the first unlock command signal is input, and drives four motors 92 corresponding to three doors other than the driver's seat door and a trunk door when the second unlock command signal is input within the predetermined time.
FIGS. 5A and 5B are time charts of signals for the unlocking operation. FIG. 5A shows a case in which the unlock switch 53b is pressed twice, for example, at an interval of one second or more, and FIG. 5B shows a case in which the unlock switch 53b is pressed twice, for example, at a short interval of 500 msec. Solid lines show first output signals, and broken lines show second output signals. As shown in FIG. 5A, when the unlock switch 53b is pressed twice at an interval of one second or more, the controller 80 receives a first unlock command signal output from the receiver 70 before the receiver 70 identifies a second unlock signal. Therefore, the two pressing operations do not interfere with each other. The driver's seat door can be unlocked by the first press, and the other doors can be unlocked at the second press.
However, when the unlock switch 53b is pressed twice, for example, at an interval of 500 msec, as shown in FIG. 5B, the receiver 70 finishes identification of a second unlock signal while outputting a first unlock command signal, and therefore, starts outputting a second unlock command signal immediately after a predetermined time. In this case, the output of the first unlock command signal is interrupted after the passage of 500 msec. The controller 80 does not determine the first unlock command signal as an authorized signal, but determines only the second unlock command signal as an authorized signal. For this reason, even when the unlock switch 53b is pressed twice, the controller 80 determines that the unlock switch 53b is pressed only once, and as a result, only the driver's seat door is unlocked.
In order to solve the above problem, it is conceivable to adjust the timing of transmission of signals from the portable transmitter, as disclosed in Japanese Unexamined Patent Application Publication No. 11-81764 (U.S. Pat. No. 6,396,389). However, this complicates the configuration of the system, and increases the cost and power consumption. Although it is also conceivable to transmit a signal after the preceding signal is completely transmitted, this causes a problem similar to the above-described problem.